The recording densities of hard disk devices (HDD), which represent one type of magnetic recording/reproducing device, are currently increasing at a rate of 50% or more every year, and it is said that this tendency is likely to continue. Accordingly, the development of magnetic heads and magnetic recording media suitable for these high recording densities also continues to progress.
Currently, the magnetic recording media installed within most commercially available magnetic recording/reproducing device are so-called perpendicular magnetic recording media in which the axis of easy magnetization within the magnetic film is mainly oriented perpendicularly. In these magnetic recording media, even when the recording density is increased, the effect of the demagnetizing field at the boundary region between recording bits is small, meaning a clear bit boundary is formed, and therefore any increase in the noise can be suppressed. Moreover, the reduction in the recording bit volume accompanying the increase in recording density can be kept to a minimum, meaning the medium is also resistant to the heat fluctuation effect. As a result, these magnetic recording media have been the focus of considerable attention in recent years, and many structures have been proposed for media that are suitable for perpendicular magnetic recording.
Further, in order to satisfy demands for even higher recording densities within magnetic recording media, the use of single-pole heads which exhibit excellent writing capabilities to perpendicular magnetic layers is also being investigated. In order to enable the use of these types of single-pole heads, so-called two-layer magnetic recording media have been proposed, in which, by providing a soft magnetic underlayer composed of a soft magnetic material between the perpendicular magnetic layer that functions as the recording layer and the non-magnetic substrate, the efficiency of the movement of magnetic flux between the single-pole head and the magnetic recording medium is improved.
In other words, in this type of two-layer magnetic recording medium, the mirror image effect of the soft magnetic underlayer has the function of strengthening the recording magnetic field from the main magnetic pole of the magnetic recording head, thereby spatially concentrating the recording magnetic field and increasing the gradient of the recording magnetic field.
However, simply using a magnetic recording medium in which a soft magnetic underlayer has been provided does not yield entirely satisfactory properties in terms of the recording and reproduction properties during recording and reproduction, the resistance to heat fluctuation and the recording resolution, and a magnetic recording medium that exhibits excellent levels of these properties is still sought.
For example, Patent Document 1 discloses a perpendicular magnetic recording medium in which a backing magnetic layer is provided on a non-magnetic substrate, and a perpendicular magnetic film and a protective lubricant film are then provided on the backing magnetic layer, wherein by antiferromagnetically coupling the backing magnetic layer, leaked magnetic flux emitted from the domain walls of the backing magnetic layer is prevented from entering the reproducing head, and the domain walls that exist within the backing magnetic layer are fixed to prevent easy movement, enabling a perpendicular magnetic recording medium with low noise characteristics to be obtained.
Further, Patent Document 2 discloses that by forming the soft magnetic layer from a plurality of layers and providing a separating layer between each of the soft magnetic layers, the magnetic permeability of the soft magnetic layer can be enhanced, and the leaked magnetic field from the magnetized transition region of the magnetic recording layer and the magnetic field from the magnetic head can be drawn into the soft magnetic layer, thereby enabling stabilization of the magnetization recorded within the magnetic recording layer and more effective extraction of the writing magnetic field from the magnetic head.
Patent Document 3 discloses a soft magnetic alloy in which Fe:Co=65:35, and also discloses the addition of Ta to this alloy.